The manufacture of silver halide photographic emulsions is usually carried out by adding silver ions and halide ions within a reactor equipped with a stirrer. The initial addition causes nucleation, and the sequent addition causes crystal growth.
Preferred silver halide grains to be used in emulsions for light-sensitive material are grains having high monodispersity of size and uniformity of shape. For this purpose, one of functions required for stirring machines is to realize uniform mixing instantaneously and microscopically.
The stirring method includes various methods as described in, for example, JP-A-7-219092 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-8-171156, JP-A-4-283741, JP-B-8-22739 (the term “JP-B” as used herein means an “examined Japanese patent publication”), and U.S. Pat. No. 3,782,954. However, in the case where the nucleation is carried out by such methods, even by employing any of the foregoing methods, the liquid is circulated within the reactor, and nucleation and nuclear growth take place in parallel, so that it is difficult to form monodispersed nuclei. For example, in the field of silver halide photography, in order to enhance light-receiving efficiency, tabular silver halide grains having a large light-receiving area are widely used as a light-sensitive element. However, in the foregoing methods, there is caused an obstacle such that during circulation of the silver halide grains within the reactor, the tabular silver halide grains that go on the way of growth pass through a high supersaturation region in the vicinity of a port of adding the silver ions or halide ions to increase the thickness of the tabular grains or cause polydispersion of the grain size, resulting in lowering of the light-receiving efficiency. Incidentally, the tabular silver halide grain is characterized by a ratio of equivalent circular diameter (diameter of a circle having the same projected area as grain) to grain thickness, i.e., an aspect ratio.
In order to solve these problems, there is a method in which besides the reactor, an external mixer is provided, silver halide fine grains are formed by the external mixer, and the formed silver halide fine grains are added in the reactor, thereby undergoing a part or the whole of the nucleation step or growth step. According to this method, a silver salt aqueous solution, a halide aqueous solution and a dispersion medium aqueous solution are added in the external mixer to continuously form fine grains. The fine grains can be used for the nucleation and/or growth. In such a method, it is desired to completely mix the added solutions in the external mixer within a short period of time as far as possible and discharge the formed fine grains out the external mixer as fast as possible. It is not preferred that a long period of time is needed for mixing or the added solutions are circulated within the external mixer.
In U.S. Pat. No. 5,250,403 or JP-A-10-43570, a method of mixing by a stirring blade in a small-volume mixer is described. However, in such a method, the added solutions are circulated in the mixer.
In JP-A-4-139440 and JP-T-6-507255 the term “JP-T” as used herein means a “published Japanese translation of a PCT patent application”), the added solutions are not circulated because mixing is carried out without mechanical stirring. However, according to these methods, a mixing force is not satisfactory because strong stirring is not performed. U.S. Pat. No. 5,104,786 or JP-A-11-38539 discloses a method in which two solutions are mixed within a pipe. In this case, the added solutions are not circulated. However, because of a so-called plug flow in which the solutions flow in a constant direction, the mixing cannot help relying on the generation of a turbulent flow accompanied with a high-speed flow. In order to generate a sufficient turbulent flow by the plug flow, it is necessary to continue a very high-speed flow, and such involves difficulty.
In order to keep a sufficient mixing force without mechanical stirring, there is a method in which the added solutions are made a linear jet flow, and mixing is carried out by its kinetic energy. JP-8-A-334848 discloses a process of production of silver halide photographic emulsions utilizing such a kinetic energy of jet flow. However, this patent document is concerned with a process of production of silver halide photographic emulsions by a single jet process, and the internal circulation time of the added solutions is large. In addition, since the kinetic energy as used therein is insufficient to perform mixing the whole of the reactor, mechanical stirring is jointly employed.
JP-A-2000-338620 or JP-A-2001-290231 discloses that at least one of a silver salt aqueous solution and a halide aqueous solution is made a high-speed linear jet flow (straight flow), and the two solutions are mixed within a short period of time to continuously form silver halide grains. However, even by utilizing the high-speed flow, such is still insufficient for microscopic mixing, and further improvements have been demanded.